It’s never too early to be booking your wedding vendors. 
OK maybe over two years is a little much, but in general it’s always to your advantage. By booking well in advance you can get much higher quality vendors because more dates will be available. This will also give you time to be guests at your friends’ weddings, read blog articles etc… You can relax knowing you got great vendors already set up for your big day. Then you can make decision based on preference instead of just availability.